The Research On Small-scale Array Signal Processing

Small-scale array has the merit to be installed easily, which the underwater vehicles are preferred to equip with. Miniaturizing the system and developing new signal processing methods to promote the ability for the small-scale array are becoming a hotspot in underwater equipment production. The limit of the underwater instruments' cubage restricts to get large array scale in some application situation, while the large scale is the key to obtain high resolution ability. It is usual to track the target in low signal to noise ratio (SNR) in the presence of many interference sources. This dissertation tries to explore the new methods for the multi-target tracing in small-scale array.The relationship between the beam space power and the correlation function in uniform linear array is analyzed first to propose a new covariance matrix and the idea of the beam space eigenvalue. The distribution of this eigenvalue is determined by the array manifold.Then the beam eigenvalue method(BEM) algorithm is discussed. Comparing with AIC and MDL algorithms, the BEM can estimate the source number in lower SNR. Incorporating with the virtual element methods, the virtual-BEM(V-BEM) algorithm is proposed for the small-scale array source number estimation. The beamforming pattern is improved by adding the virtual element to inhibit the gratinglobe.The distribution of the beam eigenvalue becomes more stable for estimation.The two methods proposed can be used not only for incoherent targets but also for coherent targets, and avoids the aperture loss caused by the space smoothing,which is very important for the small scale array.The self-noise spectrum of the ship, submarines and various underwater vehicles are high. The modern sonar is forced to work and required to promote the low SNR detectation ability in presence of strong interference. At the same time,it is also focused to trace and detect the multi-target with strong interference by using small-scale array. So based on the idea of shielding the interference direction, the inverse beamforming algorithm is designed and the relationship between the inverse beamforming matrix and beamforming matrix is deduced. The inverse beamforming using the phase-shift and time delay is presented. The interference from both larboard and starboard is cancelled simultaneously if just the pressure used; while the vector array inverse beamforming counteracting can cancel the interference in 0°～360°. The problem of distinguishing whether there is multi-target impinging or vague caused by single target could also be solve using the vector array inverse beamforming.To satisfy the work requirement of the acoustic fuze of underwater mine and some other underwater weapons, the multi-target tracking system is designed based on the small-scale vector array. The small-scale array is restricted in array aperture which causes wider side lobes. Using the fixed small array to track higher frequency targets will cause grating lobe. A group of parallel Notch filter with different frequency is used to track ship targets by the radiated noise .Through the combination of the virtual array and constant beam width technique, the gratinglobe and the phase vague problem is overcame. The system uses the virtual elements, Notch filter offline beamforming, constant beamwidth and the vector array inverse beamforming algorithm synthetically to promote the performance of the small scale vector array. The weaker target can be estimated by canceling the strong targets, even if the two targets working in the same frequency. The multitarget tracking performance can be also promoted. The simulation and experiments analysis has confirmed the ability of this system.